... is your major plugin file, which is automatically reloaded by
Sublime Text on change. The other python files within subfolders are not. This
contains your commands you export to sublime text or whatever.

On each test the module passed to run_plugin_unittest is reloaded.
So this file is responsible to reload everything, which is needed for the
test:

# this is the class, which is run by run_plugin_unittest
from imp import reload
# make sure we have got latest changes
from . import test_first_collection
reload(test_first_collection)
from . import test_second_collection
reload(test_second_collection)
from .. import some_file
reload(some_file)
# import all testcases
from .test_first_collection import *
from .test_second_collection import *